The technical field generally relates to methods of manufacturing polymer-metal nanocomposites (PMNCs) with uniform dispersion of metal nanoparticles in a polymer matrix.
PMNCs have drawn significant attention in the past two decades due to their unique physicochemical properties for functional applications, including, but not limited to, electrically conducting polymers for transparent electrodes, electromagnetic interface shielding (e.g., electromagnetic interference shielding), electrostatic dissipation, plasmonic metamaterials as electromagnetic wave absorbers for solar cells, and antimicrobial polymers. Based on the nature of the incorporation of metal nanoparticles, the fabrication methods can be divided into so-called extrinsic and intrinsic methods. For extrinsic methods, nanoparticles are prepared separately and then incorporated into the polymer matrix during processing. Nanoparticles are dispersed via some kinetic approaches such as using shear forces or ultrasonic vibrations. The surface of the metal nanoparticles are often functionalized or passivated to facilitate dispersion. A uniform dispersion of dense nanoparticles, however, is still hard to achieve. Nanoparticles tend to aggregate into larger particles due to Van der Waals attractive forces. Bulk manufacturing processes that incorporate nanoparticles directly into products have serious safety drawbacks because the small nanoparticles can rapidly combust given appropriate ignition conditions.
In contrast, extrinsic methods utilize physical deposition to produce polymer-metal nanocomposites. Unfortunately, these deposition methods generally offer a homogeneous distribution only in thin films. The intrinsic methods are basically of chemical nature as metal particles are formed in-situ during processing. These wet chemical methods, which are generally very complex, can only produce a very limited set of bulk polymer-metal nanocomposites with a reasonable dispersion of metal nanoparticles.
Thermal fiber drawing processes have recently emerged as a novel top-down nano-manufacturing process. Nano-wires of semiconductor, some amorphous metals, and polymers embedded in amorphous cladding materials, such as fused silica, Pyrex® glass and thermoplastic polymers, have been demonstrated. For example, International Patent Publication No. WO 2016/122958 discloses a method for thermally drawing fibers that contain continuous crystalline metal nanowires. However, due to the low viscosity and high surface tension of the molten metal, it is extremely difficult to obtain nanoscale metal threads/wires in the amorphous cladding (such as polymers). A scalable fabrication technique for forming polymer nanocomposites with a uniform dispersion of dense, crystalized metal nanoparticles remains a long-standing challenge.
In one embodiment, a method of forming a polymer-metal nanocomposite (PMNCs) material with a substantially uniform dispersion of metal particles in a polymer matrix includes the steps of forming a solid composite preform by mixing a blend of micrometer-sized metal particles and mixture of polymer particles and subjecting the mixture to compression followed by sintering. The composite, solid preform is then drawn through a heated zone to form a reduced size fiber. This reduced size fiber is cut into a plurality of fiber segments and a second composite preform is formed by stacking or bundling the fibers and placing the bundle in a cladding or jacket made from a polymer (which may be the same polymer material used for the polymer particles). The second composite preform is then drawn through the heated zone to form another reduced sized fiber. A third composite preform can be made in the same manner described above and then drawn through the heated zone to form yet another reduced size fiber. After the third drawing cycle, the metal particles contained in the fiber are typically nanometer sized and more uniformly dispersed within the polymer matrix. In some embodiments, however, additional cycles of the stack-and-draw process may be needed to form nanometer-sized metal particles that are uniformly dispersed in the polymer matrix. In other embodiments, only two cycles of thermal drawing are needed.
In another embodiment, a method of forming a polymer-metal nanocomposite (PMNC) material with a substantially uniform dispersion of metal particles includes: (a) forming a composite solid preform by mixing a blend of micrometer-sized metal particles and polymer particles and subjecting the mixture to compression followed by sintering; (b) drawing the composite solid preform of (a) through a heated zone to form a reduced size fiber; (c) cutting the reduced size fiber into segments and forming a next preform using the bundle of the segments; and (d) drawing the next preform through the heated zone to form a reduced fiber. Operations (c) and (d) may be repeated a plurality of times to form the final fiber.
In another embodiment, a method of forming a molded polymer-metal nanocomposite material with a substantially uniform dispersion of metal particles includes forming a blend of metal particles having a size range from 1 μm to several millimeters and polymer particles, wherein the metal particles have a melting temperature less than a decomposition temperature of the polymer. The metal and polymer blend is then subject injection molding to generate the molded polymer-metal nanocomposite material, wherein the molded polymer-metal nanocomposite material has a substantially uniform dispersion of metal particles having sizes less than 1 μm.
In another embodiment, a fiber that is created using the process described herein may be used to manufacture other structures. For example, the fiber can be woven to generate useful articles of manufacture.
The polymer particles 6 may be made from any number of thermoplastic polymer materials. The polymer particles 6 may be in the form of granules, pellets, or the like that are commercially available and may include any number of sizes and shapes. Particular examples of polymer types include, for example, polyethersulfone (PES), polysulfone (PSU), and polyethylenimine (PEI). Polymers may also include glass (e.g., Pyrex® glass) or fused silica. As explained herein, the polymer material used for the particles 6 forms a matrix that contains the reduced size metal particles 4 that are created during the thermal drawing process. The material combination of the metal particles 4 and the polymer particles 6 is chosen such that the metal particles 4 have a melting temperature that is below the degradation temperature of the polymer particles 6. The degradation temperature of the polymer particles 6 is the temperature at which the polymer begins to break down chemically or char in response to applied heat. The relative composition of metal used to form the preform 2 may vary. Typically, the mixture used to make the solid preform 2 will have less than 40% by volume of metal particles 4.
With reference to
Referring back to
Next, as seen in operation 120, the reduced diameter fiber 15 that has been drawn through the furnace 14 is then cut and placed in a bundle or stack 16. This bundle 16 of fibers 15 is then used to create an additional preform 2 as illustrated in operation 130 of FIG. 1. The process involves placing the bundle 16 of fibers 15 into a jacket 18 of cladding material. The cladding material of the jacket 18 is typically made of the same polymer material as the polymer particles 6 although other polymer materials may be used. The jacket 18 may include, for example, a cylindrical jacket 18 that is already formed. Alternatively, the jacket 18 may be formed by rolling or wrapping a flat jacket 18 around the bundle 16 of fibers 15. The jacketed material is then subject to a consolidation process where the bundle 16 of fibers 15 with the jacket 18 is heated in a tube furnace (separate from the fiber drawing furnace 14) that is conventionally known. The consolidation process heats the fibers 15 and cladding material of the jacket 18 to form a unitary preform structure 2 than can then be used in another thermal drawing process as illustrated in
As seen in
Eventually, a final fiber 50 is produced that has the desired properties as seen in operation 140. In one particular preferred embodiment, the final fiber 50 that is generated is formed with metal particles 4 formed therein of reduced diameter than those used in the initial preform 2. For instance, the final fiber 50 contains metal particles 4 that have diameters that are less than 1 μm in size (i.e., nanoparticles of metal) even though the starting preform 2 had metal particles 4 that were larger than 1 μm. In addition, the metal particles 4 are preferably dispersed in a substantially uniform manner through the polymer matrix of the final fiber 50. As seen in
As seen in
Unlike the fiber-based embodiment, in this embodiment, the mixture or blend of metal particles 4 and the polymer particles 6 (which may also include granules, pellets, or the like) of the types and sizes described herein are loaded into the hopper 202 which feeds into the barrel 208 of the injection molding system 200. The mixture is then run through the injection molding system 200 whereby the polymer particles 6 and the metal particles 4 are heated and forced through the nozzle 214 and into the mold that defines the article of manufacture 60 that is formed from the molded polymer-metal nanocomposite material. In one preferred embodiment, the material in the final molded article has substantially uniform dispersion of metal particles 4 having sizes less than 1 μm.
Note that in either the thermal drawing method or the injection molding method, the manufacturing method purposefully creates thermal capillary instability so that any wires or fibers of metal that form in the polymer matrix during thermal drawing or passage through the nozzle 214 are broken to form droplets which then solidify into the smaller nanoparticles of metal.
Composite Preform Fabrication
Non-uniform Tin (Sn) and Polyethersulfone (PES) microparticles with an average diameter of 40 μm and 60 μm, respectively, were used. The PES (95 vol. %) and Sn (5 vol. %) microparticles were first blended by a mechanical shaker for one hour. The well-blended microparticle mixture was then added to a cylindrical stainless steel mold as seen in
A longitudinal cross-section of the PES-5Sn composite perform was used to study the distribution and dispersion of Sn microparticles.
With reference to
Next, a stack-and-draw process was used as illustrated in
While this specific embodiment utilized three thermal drawing cycles it should be appreciated that fewer or more cycles may be used. For example, if larger sized particles or fibers embedded within a matrix are desired, there may only need to be one or two thermal draw cycles. In contrast, if smaller, nanometer-sized particles are desired, three or more thermal draw cycles may be used.
After the third drawing cycle, an ultramicrotome technique was used to prepare films for scanning electronic microscopy (SEM) analysis having a 500 nm thickness from the composite fiber's sidewall. The films were manually placed on carbon tape for SEM study as seen in the test setup of
PMNCs with uniform dispersion of metallic nanometer-sized particles embedded in a matrix can be used in a number of applications. For example, these materials may be used for electromagnetic interface shielding and electrostatic dissipation. Most of the current techniques to manufacture PMNCs are focused on bottom-up approach which is restricted for small batch fabrication. However, this method is a top-down manufacturing approach which allows scalable production of PMNCs. In addition, because PMNC composites are manufactured from thermoplastic materials, these fibers (or molded articles) can be used to produce any geometrical shapes. Finally, the manufacturing method described herein can be used for scalable fabrication of metal microparticles (e.g., micrometer-sized particles) and nanoparticles (e.g., nanometer-sized particles), if the polymer cladding is dissolved after the drawing cycle. For example, experiments show that Sn nanoparticles with average diameter of 46 nm and as small as 10 nm can be produced when PES cladding is dissolved away from the third cycle drawing fibers.
While embodiments of the present invention have been shown and described, various modifications may be made without departing from the scope of the present invention. The invention, therefore, should not be limited, except to the following claims, and their equivalents.
This application claims priority to U.S. Provisional Patent Application No. 62/347,382 filed on Jun. 8, 2016, which is hereby incorporated by reference in its entirety. Priority is claimed pursuant to 35 U.S.C. § 119 and any other applicable statute.
This invention was made with Government support under 1449395, awarded by the National Science Foundation. The Government has certain rights in the invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US17/36432 | 6/7/2017 | WO | 00 |
Number | Date | Country | |
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62347382 | Jun 2016 | US |